Birth and abortion rates among U.S. teens fell to record lows in 2008 as increased use of contraceptives sent the overall teen pregnancy rate to its lowest level since at least 1972, a study showed on Wednesday.

But disparities among racial and ethnic groups continued to persist, with black and Hispanic teens experiencing pregnancy and abortion rates two to four times higher than their white peers, the Guttmacher Institute, the nonprofit sexual health research group that conducted the analysis, said.

The Guttmacher researchers looked at government statistics on teen-age sex, pregnancies and births, as well as the institute’s own data on abortions for 2008, the most recent year for which all the numbers were available.

They found that nearly 750,000 U.S. women under the age of 20 became pregnant in 2008 - nearly 98 percent of them between the ages of 15 and 19.

That translated into a pregnancy rate of 67.8 pregnancies per 1,000 women aged 15 to 19, the researchers said, the lowest pregnancy rate seen since 1972, the year before the Supreme Court decision in Roe v. Wade that established a woman’s right to an abortion.

It was also down 42 percent from 1990, when teen pregnancies peaked at 116.9 per 1,000 teen girls and women.

The teen abortion rate in 2008 dropped to the lowest rate seen since 1972 at 17.8 per 1,000 teen girls and women, the analysis found, and was down 59 percent from 1988 when the abortion rate peaked at 43.5 per 1,000 teen women.

The Guttmacher researchers said the decline in teen birthrates was largely attributable to increased contraceptive use by teens of both genders.

“Teens are also using more effective forms of contraception,” said Kathryn Kost, a demographer with the Guttmacher Institute who co-authored the analysis.

Among women aged 15 to 17, about a quarter of the long-term decline in pregnancies, births and abortions could be attributable to reduced sexual activity, the researchers said.

But pregnancy, birth and abortion rates remained much higher for teens who belonged to minority groups, even though their overall rates have fallen over the past four decades.

Birth rates for black and Hispanic teens were more than twice those of their white peers in 2008, the researchers found. The abortion rate among black teens, meanwhile, was four times higher than the rate for their Caucasian counterparts. Abortion rates for Hispanic teens were twice as high as for their white peers.

The Guttmacher study was funded with grants from The California Wellness Foundation, The William and Flora Hewlett Foundation, The David and Lucile Packard Foundation and the Ford Foundation.

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By James B. Kelleher